Limit of discrimination

Fig. 4.9. Distributions of measured values which belong to the content at the limit of specification xLSp and at the screening limit Xscr dis is the limit of discrimination...

The performance curve presents graphically the relationship between the probability of obtaining positive results PPRy i.e. x > xLSp on the one hand and the content x within a region around the limit of discrimination xDIS on the other. For its construction there must be carried out a larger number of tests (n > 30) with samples of well-known content (as a rule realized by doped blank samples). As a result, curves such as shown in Fig. 4.10 will be obtained, where Fig. 4.10a shows the ideal shape that can only be imagined theoretically if infinitely exact decisions, corresponding to measured values characterized by an infinitely small confidence interval, exist. 

Colpaert, F. C., Niemegeers, C. J. E., and Janssen, P. A. J. (1980) Factors regulating drug cue sensitivity Limits of discriminability and the role of a progressively decreasing training dose in fentanyl-saline discrimination. J. Pharmacol. Exp. Ther., 212 474-480. 

Fig. 9-9 demonstrates the results of MVDA for the three investigated territories in the plane of the computed two discriminant functions. The separation line corresponds to the limits of discrimination for the highest probability. The results prove that good separation of the three territories with a similar geological background is possible by means of discriminant analysis. The misclassification rate amounts to 13.0%. The scattering radii of the 5% risk of error of the multivariate analysis of variance overlap considerably. They demonstrate also that the differences in the multivariate data structure of the three territories are only small. 

Wolfenden, R., and Kati, W. M., 1991. Testing the limits of protein-ligand binding discrimination widi transition-state analogue inhibitors. Accounts of Chemical Research 24 209-215. 

We will explore the two major families of chemometric quantitative calibration techniques that are most commonly employed the Multiple Linear Regression (MLR) techniques, and the Factor-Based Techniques. Within each family, we will review the various methods commonly employed, learn how to develop and test calibrations, and how to use the calibrations to estimate, or predict, the properties of unknown samples. We will consider the advantages and limitations of each method as well as some of the tricks and pitfalls associated with their use. While our emphasis will be on quantitative analysis, we will also touch on how these techniques are used for qualitative analysis, classification, and discriminative analysis. 

In addition to the effects discussed above, two further possible sources of discrimination peculiar to ion-molecule reactions must be considered. First, although it is known that most primary ions are formed without kinetic energy, such may not be the case for ions produced by ion molecule reactions. Secondary ions formed in exothermic ion-molecule reactions could retain a considerable fraction of the exo-thermicity as kinetic energy and diffuse from the sampling region at a rate considerably greater than predicted from the ambient temperature. The limited evidence to date (40) indicates that the kinetic energy of the product ions is small, but this may not be true for all types of reactions. 

As with in vivo voltammetry, a variety of electrochemical techniques have been used for the stripping step. Because of its simplicity, linear sweep voltammetry has enjoyed widespread use however, the detection limit of this technique is limited by charging current. Differential pulse has become popular because it discriminates against the charging current to provide considerably lower detection limits. 

The curve illustrates the sharpness of tests depending on the discrimination limit. In this way, TPR and TNR may be recognized and the unreliability region around the limit of specification can be estimated. Beyond the limits of the unreliability interval, it is possible to classify samples correctly apart... 

The main limitation of birefringence is that it only provides an averaged orientation value without any discrimination between amorphous and crystalline phases, or between the components in polymer blends, copolymers, and... 

There are two main factors that influence the selectivity of a sensor limits in discrimination of an interfering ion and upper limits in stability constant of an analyte-ionophore complex. While an ideal ionophore does not form complexes with interfering ions, too strong complexation with the primary ion leads to a massive extraction of analyte into membrane phase coupled with a coextraction of sample counter-ions, known as Donnan exclusion failure. In such cases, at high activities and lipophilicities of sample electrolytes, fli(org) increases and a breakdown of membrane permselectivity prevents the Nemst equation to hold. 

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